In order to make it worthwhile to purchase a new piece of equipment, the annual depreciation costs for the equipment cannot exceed $3000 at any time. The original cost of the equipment is $30,000, and it has zero salvage and scrap value. Determine the length of service life necessary if the equipment is depreciated
(a) by the sum-of-the-years-digits method, and
(b) by the straight-line method.